A novel strategy for force identification of nonlinear structures

Dynamic force is the key indicator for monitoring the condition of a mechanical product. These mechanical structures always encompass some nonlinear factors. Most previous studies focused on obtaining the dynamic force of linear structures. Consequently, this study focuses on the nonlinear mechanical structure, and a novel identification strategy is proposed to indirectly identify the excitation force. For the identification strategy, based on a nonlinear state-space model, a force identification equation for the nonlinear structure is built, wherein the transfer matrix consists of coefficient matrices of the nonlinear state-space model, and these coefficient matrices are calculated by a nonlinear subspace identification algorithm. Then, under the generalized cross-validation criterion, the truncated total least squares method is introduced to solve the ill-posed equation to eventually obtain the excitation force of the nonlinear structure. The identification results from two numerical simulation cases and one experimental case illustrate that the proposed identification strategy can stably and accurately identify the excitation force of nonlinear structures.

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Force Reconstruction for Nonlinear Structures in Time Domain

Annual Conference of the PHM Society ◽

10.36001/phmconf.2018.v10i1.531 ◽

2018 ◽

Vol 10 (1) ◽

Author(s):

Jie Liu ◽

Bing Li ◽

Meng Li ◽

Huihui Miao

Keyword(s):

State Space ◽

Transfer Matrix ◽

External Force ◽

State Space Model ◽

Nonlinear Structure ◽

Space Model ◽

Mechanical Structure ◽

Force Reconstruction ◽

Reconstruction Strategy ◽

Nonlinear State

With growing complexity of mechanical structure, nonlinear factors existing in the structure have drawn much attention in recent years. Meanwhile, accurate information of dynamic force is an important index for analyzing nonlinear mechanical structure. However, these data are always difficult and even impossible to be measured directly. Therefore, in this paper, a novel reconstruction strategy is proposed to calculate the external force of the nonlinear structure on the basis of measured response at the reference position. For the reconstruction strategy, the force reconstruction equation of nonlinear structure is established by the nonlinear state-space model, and nonlinear subspace identification (NSI) algorithm is utilized to estimate coefficient matrices of the nonlinear state-space model to form the transfer matrix. And then, considering the illcondition of the transfer matrix, the regularization method combined with the generalized cross-validation criterion is utilized to solve the ill-posed reconstruction equation to obtain the unknown external force. Numerical study is conducted to illustrate the feasibility of the reconstruction strategy. The results demonstrate that the proposed reconstruction strategy can be utilized to accurately obtain the external force of the nonlinear structure.

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